A constitution for driving a motor with a high efficiency using a fuel cell as the main power source is disclosed as prior art in Publication of Unexamined Japanese Patent Application No. 2002-118981. In this example, a battery is connected to the fuel cell in parallel via a DCDC converter with the intent of improving the output efficiency of the power source by controlling the DCDC converter's output voltage.
However, the total volume of the system including the power source, the power converter, and the motor is large because of the use of the DCDC converter, and the system generates a loss when charging and discharging the battery because of routing through the DCDC converter.